It is possible to observe the structure of the surface of a sample by irradiating and scanning the sample with electrons and detecting secondary charged particles emitted from the sample. This is called a scanning electron microscope (hereunder abbreviated to SEM). Meanwhile, it is also possible to observe the structure of the surface of a sample by irradiating and scanning the sample with an ion beam and detecting secondary charged particles emitted from the sample. This is called a scanning ion microscope (hereunder abbreviated to SIM). If a sample is irradiated with such kind of light-mass ions as hydrogen or helium in particular, sputtering relatively reduces and the sample can be well observed.
Here, the excitation region of secondary electrons caused by the intrusion of hydrogen or helium into a sample surface is more localized on the sample surface than the case of electron irradiation and hence the characteristic in that an SIM image is far more sensitive to sample surface information than an SEM image is expected. From the viewpoint of a microscope further, ions are heavier than electrons and hence ions are characterized in that the diffraction effect can be ignored in beam convergence and an image of a very large focal depth can be obtained.
Further, it is also possible to obtain information reflecting the internal structure of a sample by irradiating the sample with an electron beam or an ion beam and detecting the electrons or the ions having permeated the sample. This is called a transmission electron microscope or a transmission ion microscope. If a sample is irradiated with such kind of light-mass ions as hydrogen or helium in particular, the proportion of the ions permeating the sample increases and the sample can be well observed.
A gas field ion source: has a narrow ion energy width and a small ion source size; hence is expected to produce a minute beam; and is an ion source suitable for such a scanning ion microscope and a transmission ion microscope. JP-A-Sho58(1983)-85242 discloses that the ion source performance improves when a gas field ion source uses an emitter tip having a minute protrusion at the apex thereof. Further, H.-S. Kuo, I.-S. Hwang, T.-Y. Fu, J.-Y. Wu, C.-C. Chang, and T.-T. Tsong, Nano Letters 4 (2004) 2379 disclose that a minute protrusion at the apex of an emitter tip is made of a second metal that is different from the material for the emitter tip.
Furthermore, J. Morgan, J. Notte, R. Hill, and B. Ward, Microscopy Today, Jul. 14 (2006) 24 disclose a scanning ion microscope on which a gas field ion source to emit helium ions is mounted.
Yet further, JP-A-Sho63(1988)-216249 discloses a gas field ion source equipped with a cylindrical liquid nitrogen container so as to surround an ion generating section and other sections. The document also discloses a gas field ion source that: is provided with a heating means for degassing to the atmosphere side of a vacuum chamber of the gas field ion source and a cooling chamber to cool the vacuum chamber outside the heating means; and thereby reduces the consumption of liquid nitrogen.
In addition, JP-A-Hei1(1989)-221847 discloses: a selector switch to connect a high voltage line for an extraction electrode to a high voltage line for an emitter tip; and a gas field ion source that can prevent electric discharge between the emitter tip and the extraction electrode after forced discharging treatment, namely conditioning treatment, between the outer wall of the ion source and the emitter tip.
Further, there is an example of processing that uses the phenomenon wherein particles constituting a sample are emitted from the sample by the sputtering of ions when the sample is irradiated with an ion beam. It is also possible to minutely process a sample. Generally on this occasion, a focused ion beam apparatus (hereunder abbreviated to FIB apparatus) that uses a liquid metal ion source (hereunder abbreviated to LMIS) is preferably used. Furthermore, in recent years, a composite FIB-SEM apparatus formed by combining an SEM and a focused ion beam apparatus has also been used. By the FIB-SEM apparatus, it is possible to form a square hole at an intended portion by the irradiation of an FIB and observe a cross section thereof with the SEM.
For example, JP-A-2002-150990 proposes an apparatus to observe and analyze defects and foreign matters by forming a square hole in the vicinity of an abnormal portion in a sample with an FIB and observing the cross section of the square hole with an SEM.
Furthermore, WO99/05506 proposes a technology of picking up a minute sample for transmission electron microscope observation from a bulk sample with an FIB and a probe.